1. Technical Field
The present invention relates generally to an engine starting apparatus which may be installed in automotive vehicles and is designed to switch between a first power supply path in which electric power is supplied to start an engine starting motor through a resistor and a second power supply path in which the electric power is supplied to the engine starting motor without passing through the resistor after the start of the engine starting motor.
2. Background Art
When an automotive engine is started using an engine starter equipped with an electric motor, that is, when main contacts are closed by an electromagnetic switch to supply electric current from a battery to turn on the motor, a heavy current called inrush current usually flows through the motor. This causes voltage at a terminal of the battery to drop greatly briefly which may result in shutdown of other electrical devices such as indicators or audio players installed in the vehicle which are to be powered by the battery.
Japanese Patent First Publication No. 2009-287459, assigned to the same assignee as that of this application, teaches controlling the inrush current appearing upon start of the electric motor of the engine starter to avoid the shutdown of the electric devices.
FIG. 4 illustrates an engine starting system, as disclosed in the above publication. A resistor 120 is disposed in an electric power supply path through which electric current is supplied from a battery 100 to an electric motor 110. A motor relay 130 short-circuits ends of the resistor 120. A timer 140 controls the time when the motor relay 130 is to be excited or closed. Specifically, the timer 140 determines a time lag between excitation of an electromagnetic switch 150 and that of the motor relay 130 so that contacts of the motor relay 130 are closed until the time lag has elapsed after main contacts of the electromagnetic switch 150 are closed.
Specifically, the timer 140 delays the excitation of the motor relay 130 until the time lag has elapsed after the electromagnetic switch 150 is excited, thereby causing the current to flow from the battery 100 to the motor 110 through the resistor 120 during a period of time from when the main contacts are closed until the relay contacts are closed. The current lowered by the resistor 120 is, therefore, supplied to the motor 110, so that the motor 110 runs at a lower speed.
When the time lag has elapsed, for example, after a pinion 160 meshes with a ring gear 170, the motor relay 130 is closed to short-circuit the ends of the resistor 120, thereby causing full voltage of the battery 100 to be applied to the motor 110. The current higher than that when the motor 110 is started is, thus, supplied to the motor 110, so that the motor 110 runs at a higher speed.
The structure of FIG. 4, however, has the following drawback.
The main contacts of the electromagnetic switch 150 are connected in series with the relay contacts of the motor relay 130. The turning on of the motor relay 130 to short-circuit the ends of the resistor 120 after the start of the motor 110, thus, the current to flow through the relay contacts while bypassing the resistor 120, which leads to a great drop in voltage to be applied to the motor 110 because the contacts (i.e., electric resistors) are greater than those in typical engine starting systems which are not equipped with the motor relay 130. This adversely affects the startability of the engine.
When the resistor 120 is short-circuited to apply the full voltage of the battery 100 to the motor 110, the current passes through the relay contacts of the motor relay 130, thus requiring the need for the motor relay 130 to have substantially the same capacity as that of the main contacts of the electromagnetic switch 150. This results in an increase in total production cost of the engine starting system.